Physics of the early Universe is at the boundary of astronomy and
philosophy since we do not currently have a complete theory that
unifies all the fundamental forces of Nature at the moment of
Creation. In addition, there is no possibility of linking
observation or experimentation of early Universe physics to our
theories (i.e. its not possible to `build' another Universe). Our
theories are rejected or accepted based on simplicity and aesthetic
grounds, plus there power of prediction to later times, rather than
an appeal to empirical results. This is a very difference way of
doing science from previous centuries of research.

Our physics can explain most of the evolution of the Universe after
the Planck time
(approximately 10-43 seconds after
the Big Bang).

However, events before this time are undefined in our current science
and, in particular, we have no solid understanding of the origin of
the Universe (i.e. what started or `caused' the Big Bang). At best,
we can describe our efforts to date as probing around the `edges' of
our understanding in order to define what we don't understand, much
like a blind person would explore the edge of a deep hole, learning
its diameter without knowing its depth.

Unification:

One of the reasons our physics is incomplete during the Planck era is
a lack of understanding of the unification of the forces of Nature
during this time. At high energies and temperatures, the forces of
Nature become symmetric. This means the forces resemble each other
and become similar in strength, i.e. they unify.

An example of unification is to consider the interaction of the weak
and electromagnetic forces. At low energy, photons and W,Z particles
are the force carriers for the electromagnetic and weak forces. The
W and Z particles are very massive and, thus, require alot of energy
(E=mc2). At high energies, photons
take on similar energies to W and Z particles, and the forces become
unified into the electroweak force.

There is the expectation that all the nuclear forces of matter (strong,
weak and electromagnetic) unify at extremely high temperatures under a
principle known as Grand Unified Theory, an extension of quantum physics
using as yet undiscovered relationships between the strong and electroweak
forces.

The final unification resolves the relationship between quantum forces
and gravity (supergravity).

In the early Universe, the physics to predict the behavior of matter is
determined by which forces are unified and the form that they take.
The interactions just at the edge of the Planck era are ruled by
supergravity, the quantum effects of mini-black holes. After the
separation of gravity and nuclear forces, the spacetime of the Universe is
distinct from matter and radiation.

Cosmic Singularity :

One thing is clear in our framing of questions such as `How did the
Universe get started?' is that the Universe was self-creating. This is the
key separation point between theism, the philosophy that there is a God,
and naturalism, the philosophy that only natural laws and forces operate in
the world and that nothing exists beyond the natural world.
For theism interprets the Universe having a beginning, a point where it
starts to exist, as there must exist a transcendent cause, i.e. God.
Naturalism requires that there be no cause, the Universe either exists
eternally, or the origin of the Universe takes on a "no boundary" solution
(for example, space *and* time start at the Big Bang, there is no
*before*).

The origin of the Universe also involves the question of creatio ex
nihilo, creation out of nothing. Parmenides, of course, opposed
creatio ex nihilo for "nothing comes out of nothing". Major religions are
split on the issue with mainstream Christian faiths supporting the ability
of the Creator to create out of nothing (although this begs the question of
whether God Himself counts as pre-existing matter). Other faiths believe
that the Universe was constructed from pre-existing, primordial matter,
such that the pre-Universe was eternal and our "bubble" was created (Gensis
1:6 alludes to a pre-existing water that matter is constructed from).

Modern physics is perfectly happy with creatio ex nihilo meaning that
things began as a zero-energy Universe, negative energy will become dark
energy and positive energy will becomes matter. This is not a statement on
a `cause' behind the origin of the Universe, nor is it a statement on a
lack of purpose or destiny. It is simply a statement that the Universe was
emergent, that the actual of the Universe probably derived from a
indeterminate sea of potentiality that we call the quantum vacuum, whose
properties may always remain beyond our understanding.

Extrapolation from the present to the moment of Creation implies an origin
of infinite density and infinite temperature (all the Universe's mass and
energy pushed to a point of zero volume). Such a point is called the
cosmic singularity.

Infinites are unacceptable as physical descriptions, but our
hypothetical observers back at the beginning of time are protected by
the principle of cosmic censorship. What this means is that
singularities exists only mathematically and not as a physical
reality that we can observe or measure. Nature's solution to this
problem are things like the event horizon around black holes.
Barriers built by relativity to prevent observation of a
singularity.

While observations beyond the event horizon are impossible, testable
science does not for we can build models of the behavior inside the event
horizon then look for observable predictions from those models. For
cosmology, one such model for the cosmic singularity is the Hartle-Hawking
no-boundary cosmology. In this model, there is no "before" the Big Bang
because the Universe existed in imaginary time. Imaginary time is a
concept derived from quantum mechanics and is essential in connecting
quantum mechanics with statistical mechanics.
Imaginary time can be difficult to visualize. If we imagine "regular time"
as a horizontal line running between "past" in one direction and "future"
in the other, then imaginary time would run perpendicular to this line as
the imaginary numbers run perpendicular to the real numbers in the complex
plane. Imaginary time is not imaginary in the sense that it is unreal or
made-up, it simply runs in a direction different from the type of time
we experience. In essence, imaginary time is a way of looking at the time
dimension as if it were a dimension of space: you can move forward and
backward along imaginary time, just like you can move right and left in
space. Thus, the no-boundary model states that the universe is infinitely
finite: that there was no time before the Big Bang because time did not
exist before the formation of spacetime associated with the Big Bang and
subsequent expansion of the universe in space and time.

Hartle-Hawking model says that if we could travel backward in time toward
the beginning of the universe, we would note that quite near what might
have otherwise been the beginning, time gives way to space such that at
first there is only space and no time. Beginnings are entities that have to
do with time; because time did not exist before the Big Bang, the concept
of a beginning of the universe is meaningless. According to the
HartleHawking proposal, the universe has no origin as we would understand
it: the universe was a singularity in both space and time, pre-Big Bang.
Thus, the Hartle-Hawking state universe has no beginning, but it is not the
steady state universe; it simply has no initial boundaries in time
nor space.

Planck Era :

The earliest moments of Creation are where our modern physics
breakdown, where `breakdown' means that our theories and laws have no
ability to describe or predict the behavior of the early Universe.
Our everyday notions of space and time cease to be valid.

Although we have little knowledge of the Universe before the Planck
time, only speculation, we can calculate when this era ends and when
our physics begins. The hot Big Bang model, together with the ideas
of modern particle physics, provides a sound framework for sensible
speculation back to the Planck era. This occurs when the Universe is
at the Planck scale in its expansion.

Remember, there is no `outside' to the Universe. So one can only measure
the size of the Universe much like you measure the radius of the Earth.
You don't dig a hole in the Earth and lower a tape measure, you measure
the circumference (take an airplane ride) of the Earth and divide by
2iπ (i.e. C = 2π radius).

The Universe expands from the moment of the Big Bang, but until the
Universe reaches the size of the Planck scale, there is no time or
space. Time remains undefined, space is compactified. String theory
maintains that the Universe had 10 dimensions during the Planck era,
which collapses into 4 at the end of the Planck era (think of those
extra 6 dimensions as being very, very small hyperspheres inbetween
the space between elementary particles, 4 big dimensions and 6 little
tiny ones).

During the Planck era, the Universe can be best described as a
quantum foam of 10 dimensions containing Planck length sized black
holes continuously being created and annihilated with no cause or
effect. In other words, try not to think about this era in normal
terms.

Spacetime Foam :

The first moments after the Planck era are dominated by conditions
were spacetime itself is twisted and distorted by the pressures of
the extremely small and dense Universe.

Most of these black holes and wormholes are leftover from the Planck
era, remnants of the event horizon that protected the cosmic
singularity. These conditions are hostile to any organization or
structure not protected by an event horizon. Thus, at this early
time, black holes are the only units that can survive intact under
these conditions, and serve as the first building blocks of structure
in the Universe, the first `things' that have individuality.

Matter arises at the end of the spacetime foam epoch as the result of
strings, or loops in spacetime. The transformation is from
ripping spacetime foam into black holes, which then transmute into
elementary particles. Thus, there is a difference between something
of matter and nothing of spacetime, but it is purely geometrical and
there is nothing behind the geometry. Matter during this era is often
called GUT matter to symbolize its difference from quarks and leptons
and its existence under GUT forces.

Hawking Radiation:

Hawking, an English
theoretical physicist, was one of the first to consider the details
of the behavior of a black hole whose Schwarzschild radius was on the
level of an atom. These black holes are not necessarily low mass, for
example, it requires 1 billion tons of matter to make a black hole
the size of a proton. But their small size means that their behavior
is a mix of quantum mechanics rather than relativity.

Before black holes were discovered it was know that the collision of two
photons can cause pair
production. This a direct example of converting energy into mass
(unlike fission or fusion which turn mass into energy). Pair production
is one of the primary methods of forming matter in the early Universe.

Note that pair production is symmetric in that a matter and antimatter
particle are produced (an electron and an anti-electron (positron) in
the above example).

Hawking showed that the strong gravitational gradients (tides) near black
holes can also lead to pair production. In this case, the
gravitational energy of the black hole is converted into particles.

If the matter/anti-matter particle pair is produced below the event
horizon, then particles remain trapped within the black hole. But, if
the pair is produced above the event horizon, it is possible for one
member to fall back into the black hole, the other to escape into
space. Thus, the black hole can lose mass by a quantum mechanical
process of pair production outside of the event horizon.

The rate of pair production is stronger when the curvature of spacetime is high.
Small black holes have high curvature, so the rate of pair production is
inversely proportional to the mass of the black hole (this means its
faster for smaller black holes). Thus, Hawking was able to show that the
mini or primordial black holes expected to form in the early Universe have
since disintegrated, resolving the dilemma of where all such mini-black
holes are today.